<ul class='dot-change-bg'>
  <li>
      <span class='active-dot' #firDot (click)='changBg(0)'>1</span>
  </li>
  <li>
      <span #secDot (click)='changBg(1)'>2</span>
  </li>
  <li>
      <span #thiDot (click)='changBg(2)'>2</span>
  </li>
  <li >
      <span #fouDot (click)='changBg(3)'>2</span>
  </li>
  
</ul>